1. Field of the Invention
The present invention relates to a photocurable composition, and more particularly, to a photocurable composition which is sensitive to light with a wavelength ranging from the ultraviolet .region to the infrared region.
2. Description of the Related Art
Conventionally, image recording has been performed, for example, by irradiating light onto a photosensitive recording medium having a photocurable composition coated on the surface thereof based on image information, whereby the composition is cured only at an exposed area to record the image on the recording medium.
Various kinds of photocurable compositions used for such a medium are known. The photocurable compositions include a compound having a radical-polymerizable unsaturated group as a base material, a photopolymerization initiator, a sensitizer, and the like.
A composition of Benzil, Michler's ketone, diethylthioxanthone, benzophenone, and acetophenone is used alone as a photopolymerization initiator. There are also many composite type photopolymerization initiators, as follows:
(1) a dye/aliphatic amine composite system as described in JP-B-44-20189 (The term "JP-B" therein used means "an examined published Japanese patent publication. The Japanese patent publication of JP-B-44-20189 corresponds to U.S. Pats. Nos. 3,495,987, 3,479,185, 3,418,118 and 2,588,899);
(2) a hexaarylbiimidazole/radical-forming agent/dye composite system as described in JP-B-45-37377 (The Japanese patent publication of JP-B-45-37377 corresponds to U.S. Pats. Nos. 3,495,987, 3,479,185, 3,418,118 and 2,588,899);
(3) a hexaarylbiimidazole/p-dialkylaminobenzylidene ketone composite system as described in JP-A-47-2528 (the term "JP-A" herein used means "an unexamined Japanese patent application") (The Japanese patent publication JP-A-47-2528 corresponds to U.S. Pat. No. 3,652,275);
(4) a cyclic cis-.alpha.-dicarbonyl compound/dye composite system as described in JP-A-48-84183 (The Japanese patent publication JP-A-48-84183 corresponds to U.S. Pat. No. 3,756,827 and U.S. Pat. Re. No. 28,789);
(5) a carbonyl compound/tertiary amine composite system as described in JP-A-52-134692;
(6) a substituted triazine/merocyanine dye composite system as described in JP-A-54-151024;
(7) a biimidazole/indanone composite system as described in JP-A-54-155292;
(8) a hexaarylbiimidazole/p-dialkylaminostilbene derivative composite system as described in JP-A-57-21401;
(9) a hexaarylbiimidazole/p-alkylaminocinnamylidene derivative composite system as described in JP-A-58-19315;
(10) a triazine derivative/cyanine dye composite system as described in JP-A-58-29803;
(11) a triazine derivative/thiapyrylium salt composite system as described in JP-A-58-40302;
(12) a hexaarylbiimidazole/n-dialkylaminostilbene derivative composite system or a p-dialkylaminophenylbutadienyl derivative/thiol compound composite system as described in JP-A-59-56403 (The Japanese patent publication JP-A-59-56403 corresponds to U.S. Pat. No. 4,985,470);
(13) a ketone-substituted derivative/organic peroxide composite system as described in JP-A-60-32801;
(14) an .alpha.-diketone/mercaptocarboxylic acid composite system as described in JP-A-61-258802 (The Japanese patent publication JP-A-61-258802 corresponds to U.S. Pat. No. 4,777,190); and
(15) an .alpha.-diketone/polysulfide composite system as described in JP-A-61-258803 (The Japanese patent publication JP-A-61-258803 corresponds to U.S. Pat. No. 4,777,190).
However, the photocurable compositions comprising the above conventional photopolymerization initiators which are used alone are designed to act upon irradiation of light having a wavelength of 400 nm or shorter, which is close to the lower end of the visible region.
The photocurable composition comprising the composite type photopolymerization or the photopolymerization initiators which are used alone have various drawbacks characterized by, for example, a low sensitivity for photopolymerization and a low curing speed. Therefore, they require a long time for image recording.